An Upper Limit to the Dry Merger Rate at z ~ 0.55

The Astronomical Journal (Impact Factor: 4.02). 01/2010; 139(2):794. DOI: 10.1088/0004-6256/139/2/794
Source: arXiv


We measure the fraction of Luminous Red Galaxies (LRGs) in dynamically close
pairs (with projected separation less than 20 $h^{-1}$ kpc and velocity
difference less than 500 km s$^{-1}$) to estimate the dry merger rate for
galaxies with $-23 < M(r)_{k+e,z=0.2} +5 \log h < -21.5$ and $0.45 < z < 0.65$
in the 2dF-SDSS LRG and QSO (2SLAQ) redshift survey. For galaxies with a
luminosity ratio of $1:4$ or greater we determine a $5\sigma$ upper limit to
the merger fraction of 1.0% and a merger rate of $< 0.8 \times 10^{-5}$
Mpc$^{-3}$ Gyr$^{-1}$ (assuming that all pairs merge on the shortest possible
timescale set by dynamical friction). This is significantly smaller than
predicted by theoretical models and suggests that major dry mergers do not
contribute to the formation of the red sequence at $z < 0.7$.

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